The disclosure of Japanese Patent Application No. 2001-278184 filed on Sep. 13, 2001, and No. 2001-278188 file on Sep. 13, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a vehicular lockup clutch-equipped transmission control apparatus and a control method thereof. More particularly, the invention relates to control regarding a cabin heater apparatus.
2. Description of the Related Art
Transmissions in which a torque converter for transmitting power via a fluid, such as oil or the like, is provided in a power transmission path between an engine and a wheel are adopted in many conventional vehicles, including motor vehicles and the like. A type of torque converter has a lockup clutch that is hydraulically driven so as to engage an input side and an output side of the torque converter. In this type of torque converter, the lockup clutch is appropriately engaged in accordance with the state of operation of the vehicle so as to reduce the deterioration of power transfer efficiency caused by transmission of power using fluid.
However, if the hydraulic oil used to drive the lockup clutch has low temperature, responsiveness deterioration occurs in the driving of the lockup clutch for engaging the input side and the output side of the torque converter. Due to such responsiveness deterioration and the like, shock occurs at the time of engagement of the lockup clutch, and therefore adversely affects drivability, particularly when the vehicle speed is low.
Therefore, Japanese Patent Application Laid-Open No. 2-261965 and No. 62-137467, as for example, indicate that when the hydraulic oil temperature is low or the engine cooling water temperature, which is a parameter related to the hydraulic oil temperature, is low, an operation region in which the lockup clutch is engaged is reduced by changing the region to a high-vehicle speed side. Furthermore, Japanese Utility Model Application Laid-Open No. 5-83323 proposes a technology in which a heat exchanger for exchange of heat between engine cooling water and the aforementioned hydraulic oil is provided in a vehicle and the hydraulic oil temperature is raised by the heat exchanger. This technology reduces the deterioration of low-vehicle speed drivability caused by responsiveness deterioration of the lockup clutch or the like.
In order to improve the engine fuel economy, it is preferable that the lockup clutch be engaged on as many occasions as possible. Therefore, according to the conventional art, the vehicle operation region in which the lockup clutch is engaged is expanded to a low-vehicle speed side as much as possible provided that drivability is not adversely affected.
However, if the lockup clutch is engaged on an increased number of occasions, the amount of heat produced by the engine at the time of the engine operation to output a predetermined vehicle drive power decreases because the engagement of the lockup clutch improves efficiency of power transfer between the engine and the wheels. Furthermore, if the hydraulic oil temperature is raised through heat exchange via the heat exchanger, the engine cooling water loses heat to the hydraulic oil. Therefore, in a vehicle equipped with a heater apparatus for heating the cabin by heat from the engine, the heating capability of the heater apparatus decreases on some occasions due to the aforementioned reduction in the amount of heat produced by the engine or the reduction in the amount of engine-originated heat that is available for the heating. Thus, there is a possibility of insufficient heating capability of the heater apparatus at the time of engine warm-up in wintertime, or the like.
In a vehicle equipped with a heat exchanger for the hydraulic oil (also termed ATF (automatic transmission fluid) warmer, or simply termed warmer), it becomes possible to operate the lockup clutch at an early stage, that is, a low-vehicle speed stage. However, if the lockup clutch is operated in an early stage, the amount of heat produced by the engine decreases as mentioned above, so that at the heater apparatus side, it becomes less easy to raise the temperature of a medium for heating air. Thus, the heating capability of the heater apparatus decreases. Hence, there is a possibility of insufficient heating capability of the heater apparatus when high heating capability is requested at the time of engine warm-up in wintertime and the like.
The invention has been accomplished in view of the aforementioned problems. It is an object of the invention to provide a vehicular lockup clutch-equipped transmission control apparatus capable of reducing deterioration of the heating capability of a heater apparatus while improving the engine fuel economy, and a control method thereof.
In order to achieve the aforementioned object, one aspect of the invention provides a vehicular lockup clutch-equipped transmission control apparatus which is applied to a vehicle that includes a heater apparatus for heating a cabin by heat from an engine, a transmission that transfers power between the engine and a wheel, and a heat exchanger that conducts heat exchange between the engine and the transmission, and which controls a lockup clutch that is disposed between the engine and the transmission and that mechanically connects and disconnects a path of power, in accordance with a state of operation of the vehicle. The control apparatus includes a controller that determines whether a heating capability requested of the heater apparatus is at least a first predetermined level based on a parameter related to a temperature inside the cabin, and that restricts engagement of the lockup clutch if it is determined that the heating capability requested of the heater apparatus is at least the first predetermined level.
According to another aspect of the invention, there is provided a vehicular lockup clutch-equipped transmission control method which is applied to a vehicle that includes a heater apparatus for heating a cabin by heat from an engine, a transmission that transfers power between the engine and a wheel, and a heat exchanger that conducts heat exchange between the engine and the transmission, and which controls a lockup clutch that is disposed between the engine and the transmission and that mechanically connects and disconnects a path of power, in accordance with a state of operation of the vehicle. In the control method, it is determined whether a heating capability requested of the heater apparatus is at least a first predetermined level based on a parameter related to a temperature inside the cabin. If it is determined that the heating capability requested of the heater apparatus is at least the first predetermined level, engagement of the lockup clutch is restricted.
If a design is made such that the occasion of engagement of the lockup clutch is increased in number or rate in order to improve the fuel economy of the engine, the efficiency of power transfer between the engine and the wheel improves. Therefore, the engine produces a reduced amount of heat, which is disadvantageous in securing a certain heating capability of the heater apparatus. However, according to the control apparatus and the control method described above, if the heating capability requested of the heater apparatus is at or above the first predetermined level, engagement of the lockup clutch is restricted, so that the aforementioned reduction in the amount of engine-produced heat is lessened. Therefore, it becomes possible to lessen the reduction in the heating capability of the heater apparatus while improving the fuel economy of the engine.